The present invention pertains to prosthetic devices. More particularly, the invention pertains to self-centering knee joint prostheses which may be surgically implanted between the femoral condyle and tibial plateau of the knee.
Articular cartilage and meniscal cartilage provide the mobile weight bearing surfaces of the knee joint. Damage to these surfaces is generally due to genetic predisposition, trauma, and/or aging. The result is usually the development of chondromalacia, thinning and softening of the articular cartilage, and degenerative tearing of the meniscal cartilage. Various methods of treatment are available to treat these disease processes. Each option usually has specific indications and is accompanied by a list of benefits and deficiencies that may be compared to other options. Nonsteroidal anti-inflammatory drugs (NSAIDS), cortisone injections, arthroscopic debridement, osteotomy, unicompartmental knee replacement, and total knee replacement have all been used to treat the disease depending on the severity of the process.
Currently, there is a void in options used to treat the relatively young patient with moderate to severe chondromalacia involving mainly one compartment of the knee. Some patients cannot tolerate or do not want the risk of potential side effects of NSAIDS. Repeated cortisone injections actually weaken articular cartilage after a long period of time. Arthroscopic debridement alone frequently does not provide long lasting relief of symptoms. Unicompartmental and bicompartmental total knee replacements resect significant amounts of bone and may require revision surgery when mechanical failure occurs. Revision total knee replacement surgery is usually extensive and results in predictably diminished mechanical life expectancy. Therefore, it is best to delay this type of bone resecting surgery as long as possible.
Several approaches have generally been employed in the past to correct the aforementioned problems. The first approach involves repair of articular or meniscal cartilage. Repair of the articular cartilage by surgically transplanting autogenous or autologous osteochondral core grafts has had limited success, but is not always indicated. Meniscus repair using barbed xe2x80x9carrowsxe2x80x9d such as the Bionix xe2x80x9cMeniscus Arrowxe2x80x9d has been used for xe2x80x9cbucket-handlexe2x80x9d tears, but is not applicable to other knee joint problems. Thus, these methods have limited scope and are generally confined to unique kinds of damage.
In the second approach, a unicompartmental or bicompartmental bone resection is performed, replacing the bone with a load bearing prosthesis. This resection may be performed only on the femoral condyle, or may include the tibial plateau. In either case, the resection involves considerable surgical skill, and results in prosthetic devices physically anchored into the bone structure. Not only is such reconstruction expensive major surgery, but moreover, the mechanical means of attachment may fail as the patient grows older. Examples of prostheses utilized in such methods are those disclosed in Ries, U.S. Pat. No. 5,549,688; Cloutier, U.S. Pat. No. 4,207,627; and Shah, U.S. Pat. No. 5,263,987.
The third approach has been to replace the meniscal cartilage (xe2x80x9cmeniscusxe2x80x9d) with a soft, compliant material. In theory, such devices cushion the femoral and tibial bearings surfaces and distribute loads uniformly over a large portion of the knee joint due to the ability of these devices to elastically deform. This ability to deform can also be a detriment, however, when it is desired to isolate portions of the articular cartilage or bone surfaces from loads. Moreover, such devices are prone to tearing or disintegration under repeated stress due to their low tensile strength and modulus. Being flexible, they may be ejected from the meniscular cavity if not anchored in place. Anchoring devices may create an area susceptible to fatigue fracture, causing dislocation of the prosthesis and further damage to the knee joint.
Thus, for example, Kenny, in U.S. Pat. No. 4,344,193, discloses a meniscus prosthetic device of a rubbery material such as silicone rubber, having two prominences, which interact with a space defined by the geometry of the femoral condyles. This interaction involving the prominences, together with surgical sutures secured to surrounding soft tissue, are said to maintain the meniscus fixed in the proper location. A porous border, into which fibrous tissue ingrowth is theorized to occur, may also assist in performing the locating function. A similar approach is disclosed in Stone, U.S. Pat. Nos. 4,880,429; 5,007,934; and 5,158,574, where the meniscus comprises a porous matrix of biocompatible fibers or fibers of natural origin to act as a xe2x80x9cscaffoldxe2x80x9d for regrowth of native meniscal tissue. The device is manufactured with an outer contour substantially the same as that of a native meniscus.
In Kenny, U.S. Pat. No. 5,171,322, a meniscus prosthetic device is composed of a biocompatible, deformable, flexible and resilient material having the shape of a natural meniscus, but having a tail which may extend through holes bored in the bone to anchor the device. In similar fashion, Wall, in U.S. Pat. No. 4,502,161, discloses an extra-articular extension attached to the bone outside the joint; while Richmond, U.S. Pat. No. 4,919,667 employs natural fibrous growth to positively anchor his device, again shaped like a natural meniscus. Schwartz, U.S. Pat. No. 5,344,459 utilizes a soft device of rings that are inflatable with air, liquid, or semisolid to provide a gel cushion between joint surfaces.
The previously described devices of the prior art second approach all utilize soft, cushiony materials which are anchored in place by mechanical means or through tissue regrowth to prevent movement of the device or its extrusion (spitting) from the compartments. One device which differs from those previously described, and which has been used in knee reconstruction, is the so-called xe2x80x9cMacIntosh knee,xe2x80x9d where a hard prosthesis is located by means of protruding ridges, generally in the form of a cross, which nest into corresponding grooves cut into the tibial plateau to prevent movement of the device. These devices have been found to cause pain in the knee joint. This type of prosthetic device and the so-called xe2x80x9cMcKeeverxe2x80x9d device require very invasive surgical procedures, require large arthrotomy, require bone and tissue resection, and are irreversible processes.
The present invention pertains to a meniscal device suitable for surgical implantation into a knee compartment defined by the space between a femoral condyle and the respective tibial plateau. The device is a hard, self-centering meniscal device devoid of physical means that fix its location. The device does not have the natural shape of the meniscus, but rather is designed such that articulation of the knee results in a modest amount of lateral/medial and anterior/posterior translation, relative to the tibial plateau, of the device. The present invention also pertains to a process for the manufacture of suitable meniscal devices.